Chlorinated methanes such as methyl chloride, methylene chloride, chloroform, and carbon tetrachloride are commonly used as chemical reactants, solvents, propellants, and herbicides. One common method of preparing chlorinated methanes is to directly chlorinate methane, while another common method involves the hydrochlorination of methanol to produce methyl chloride, which is further chlorinated to provide the desired end product(s). Though the direct chlorination of methane is economically advantageous, the hydrochlorination of methanol is more common.
The primary reason direct chlorination is not more widely used can be attributed to the fact that methane (i.e., natural gas) is typically not pure. Natural gas normally contains other components, such as ethane and higher alkanes. Once chlorinated, such components can be difficult to remove from a process stream comprising chlorinated methanes. As an illustrative example, 1,1,-dichloroethane, produced via the chlorination of ethane, is difficult to separate from chloroform on an industrial process scale, because their boiling points are similar: 1,1-dichloroethane's boiling point is 135° F. (or 57.2° C.), while chloroform's boiling point is 142.2° F. (or 61.2° C.).
Purifying natural gas by removing components such as ethane from the methane feed stream is expensive and requires energy-intensive cold box or other purification technologies. In order to use methane in the production of high-quality chlorinated methanes, low levels of these impurities are needed. Using high purity methane in a direct chlorination reaction will produce high purity chlorinated methanes, but again, obtaining the high purity methane is expensive.
A process for the production of chlorinated methanes via the direct chlorination of an inexpensive methane gas feed stock, such as natural gas, is needed. Such a process would avoid expensive methane purification techniques, and would lower the production costs associated with the formation of chlorinated methanes.